Characteristics and pyrolysis dynamic behaviors of hydrothermally treated micro crystalline cellulose

This paper describes the application of innovative hydrothermal technology on cellulose to produce power-like solid products appropriate for pyrolysis. The hydrothermal treatment (HT) was carried out in a batch reactor in the temperature range from 250 °C to 350 °C for 2 min. The effect of HT on the characteristics of samples was explored by FTIR, XRD, and SEM analyses. The pyrolysis behaviors of the samples obtained from HT were determined by investigating the samples weight loss (TG) and the rate of weight loss (DTG) through thermogravimetric analysis (TGA) in a steam of N2 from ambient to 500 °C under the heating rate of 10 °C/min. Kinetic parameters were obtained by Coats–Redfern method and used to model the TG curve. The results show that the HT is capable for converting cellulose to carbon-rich products having a high energy density. The cellulosic crosslink and crystalline structure is broken in the HT process especially at higher temperature. The TGA results confirmed that product obtained from HT at 250 °C is more suitable for the pyroylsis than other samples with the max rates of mass loss (3.12%/°C) and conversion rate 99.91%. There was one decomposition stage in the pyrolysis of cellulose, while the HT products have two weight loss stages. The pyrolysis process can be described by one or two first-order reaction for cellulose and HT products, respectively. The obtained activation energy for second stage pyrolysis was comparably higher than that for the first stage. Depolymerisation dominates HT products obtained at 250 °C in the pyrolysis process and repolymerisation results in the formation of secondary char for HT products obtained at higher temperature. The experiments results help to understand and predict the pyrolysis behaviors and propose pre-treatment technology for practical biomass.

► The HT is suitable for converting cellulose into powder product with high energy density and good hydrophobic characteristics.
► The weight loss of HT sample obtained at 250 °C is 99.91%, which proves that HT can remarkably enhance the performance of the pyrolysis.
► HT products appear in two stair-stepping stages and activation energy of secondary stage pyrolysis is quite higher than that of first stage.